Closes #10851: New staging mechanism (#10890)

* WIP

* Convert checkout() context manager to a class

* Misc cleanup

* Drop unique constraint from Change model

* Extend staging tests

* Misc cleanup

* Incorporate M2M changes

* Don't cancel wipe out creation records when an object is deleted

* Rename Change to StagedChange

* Add documentation for change staging

netbox/extras/models/__init__.py

@@ -3,9 +3,11 @@ from .configcontexts import ConfigContext, ConfigContextModel
 from .customfields import CustomField
 from .models import *
 from .search import *
+from .staging import *
 from .tags import Tag, TaggedItem
 
 __all__ = (
+    'Branch',
     'CachedValue',
     'ConfigContext',
     'ConfigContextModel',
@@ -20,6 +22,7 @@ __all__ = (
     'Report',
     'SavedFilter',
     'Script',
+    'StagedChange',
     'Tag',
     'TaggedItem',
     'Webhook',

netbox/extras/models/staging.py

@@ -0,0 +1,114 @@
+import logging
+
+from django.contrib.auth import get_user_model
+from django.contrib.contenttypes.fields import GenericForeignKey
+from django.contrib.contenttypes.models import ContentType
+from django.db import models, transaction
+
+from extras.choices import ChangeActionChoices
+from netbox.models import ChangeLoggedModel
+from utilities.utils import deserialize_object
+
+__all__ = (
+    'Branch',
+    'StagedChange',
+)
+
+logger = logging.getLogger('netbox.staging')
+
+
+class Branch(ChangeLoggedModel):
+    """
+    A collection of related StagedChanges.
+    """
+    name = models.CharField(
+        max_length=100,
+        unique=True
+    )
+    description = models.CharField(
+        max_length=200,
+        blank=True
+    )
+    user = models.ForeignKey(
+        to=get_user_model(),
+        on_delete=models.SET_NULL,
+        blank=True,
+        null=True
+    )
+
+    class Meta:
+        ordering = ('name',)
+
+    def __str__(self):
+        return f'{self.name} ({self.pk})'
+
+    def merge(self):
+        logger.info(f'Merging changes in branch {self}')
+        with transaction.atomic():
+            for change in self.staged_changes.all():
+                change.apply()
+        self.staged_changes.all().delete()
+
+
+class StagedChange(ChangeLoggedModel):
+    """
+    The prepared creation, modification, or deletion of an object to be applied to the active database at a
+    future point.
+    """
+    branch = models.ForeignKey(
+        to=Branch,
+        on_delete=models.CASCADE,
+        related_name='staged_changes'
+    )
+    action = models.CharField(
+        max_length=20,
+        choices=ChangeActionChoices
+    )
+    object_type = models.ForeignKey(
+        to=ContentType,
+        on_delete=models.CASCADE,
+        related_name='+'
+    )
+    object_id = models.PositiveBigIntegerField(
+        blank=True,
+        null=True
+    )
+    object = GenericForeignKey(
+        ct_field='object_type',
+        fk_field='object_id'
+    )
+    data = models.JSONField(
+        blank=True,
+        null=True
+    )
+
+    class Meta:
+        ordering = ('pk',)
+
+    def __str__(self):
+        action = self.get_action_display()
+        app_label, model_name = self.object_type.natural_key()
+        return f"{action} {app_label}.{model_name} ({self.object_id})"
+
+    @property
+    def model(self):
+        return self.object_type.model_class()
+
+    def apply(self):
+        """
+        Apply the staged create/update/delete action to the database.
+        """
+        if self.action == ChangeActionChoices.ACTION_CREATE:
+            instance = deserialize_object(self.model, self.data, pk=self.object_id)
+            logger.info(f'Creating {self.model._meta.verbose_name} {instance}')
+            instance.save()
+
+        if self.action == ChangeActionChoices.ACTION_UPDATE:
+            instance = deserialize_object(self.model, self.data, pk=self.object_id)
+            logger.info(f'Updating {self.model._meta.verbose_name} {instance}')
+            instance.save()
+
+        if self.action == ChangeActionChoices.ACTION_DELETE:
+            instance = self.model.objects.get(pk=self.object_id)
+            logger.info(f'Deleting {self.model._meta.verbose_name} {instance}')
+            instance.delete()